Sweetening hydrocarbon oils



@WML M, Q D, TEN HAVE $763,594

I SWEETENING HYDROCARBON OILS Filed March l0, 1954 Cmsol E l0 I5 7.0 15 BQ 55 Mn.

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SWEETENING HYDROCARBON OILS Cornelis David Ten Have, Amsterdam, Netherlands, assignor to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application March 1t), 1954, Serial No. 415,237 Claims priority, application Netherlands March 12, 1953 6 Claims. (Cl. 19d-32) This invention relates to a method for the direct sweetening of hydrocarbon oils containing acidic sulfur compounds. More particularly, it relates to a method for converting acidic and malodorous mercaptans in petroleum hydrocarbon fractions into organic disulfdes, and especially `to such a method for the treatment of petroleum hydrocarbon fractions which contain a relatively small proportion of such undesirable sulfur compounds.

It is a well known commercial practice to extract mercaptans from hydrocarbon oils by means of an aqueous solution of an alkali metal hydroxide and a solutizer such as an alkali metal phenolate and/or an alkali metal organic carboxyiate, such as naphthenates, butyrates, and the like. The resulting spent caustic extraction solution is usually regenerated by stripping the mercaptans therefrom, as by steam stripping, or by oxidation with air, usually in the presence of an oxidation catalyst.

lt is further known (cf. U. S. Patents 2,015,038 and 2,550,965) that the mercaptans present in hydrocarbon oils can be oxidized to disuldes if the hydrocarbon oil is brought into Contact, in the presence of an oxidizing agent, for example oxygen, with an alkali metal hydroxide solution containing a comparatively small amount of a special type of phenol which is active as oxidation catalyst, particularly a polyhydrlc phenol or aminophenol having the hydroxyl groups or the hydroxyl and amino groups in the ortho or para position with respect to each other. According to U. S. Patent 2,559,905, the aqueous alkali metal hydroxide solution may also contain cresols and xylenols which promote the solubility of mercaptans in the aqueous alkali metal hydroxide solution.

With methods 'by which rnercaptans present in hydrocarbon oils, particularly in gasoline or kerosene, are oxidized to disuldes by contacting the oil with an 'aqueous alkali metal hydroxide solution in the presence of oxygen, the oxidation itself takes place in the aqueous alkali metal hydroxide solution. The mercaptans are first extracted from the hydrocarbon oil by thealkali metal hydroxide solution and in this solution, in which they are present as mercaptides, they are oxidized by the oxygen present to disuldes which then pass into the hydrocarbon oil. At the same time, the oxygen, being much more soluble in the oil than in the aqueous solution, is supplied to the aqueous solution for the oxidation primarily via the oil. However, the transfer of oxygen from the hydrocarbon oil to the aqueous alkali metal hydroxide solution proceeds with relative difficulty.

It has now been found that the oxidation of mercaptans to disuldes in processes of the type referred to in the preceding paragraph proceeds considerably more rapidly when using aqueous alkali metal hydroxide solutions which contain phenolates and which have a water content of not over 54% by volume than when using such solutions with a water content greater than 54% by volume. The percentage by volume is calculated from the percentage by weight of the water multiplied by the specific gravity of the solution.

The rates for the oxidation of mercaptans (mercaptides) to disullides brought about by means of oxygen in a two-phase system, one phase being a light hydrocarbon oil, particularly gasoline or kerosene, and the other being an aqueous solution containing an alkali metal hydroxide and a phenolate, may be classified into two groups, namely group with low oxidation rates and a group with hi 'i oxidation rates. The low oxidation rates are obtained with the phenolate-containing alkali metal hydioxide solutions having a water content of more than 54% by volume, while the high oxidation rates are ob tained with the phenolate-containing alkali metal hydroxide solutions having a water content of 54% by volume or less.

The alkali metal phenolates (phenates) in the present alkali metal hydroxide solutions may be derived from ui'tsubstituted phenol or from monohydric alkylphenols, such as phenol, o, mand p-cresols, the various xylenol isomers, ethylphenols, the propylphenols, and mixtures thereof, the alkyl groups of which contain no more than three carbon atoms in total; these phenols are understood to be otherwise unsubstituted. The individual phenolates and alkylphenolates and mixtures thereof will be referred to hereinafter by the generic designation phenolate The stable aqueous solutions of phenolate and alkali metal hydroxide with a maximum water content of 54% by volume, i. e. the solutions which are neither supersaturated in phenola-te nor in alkali metal hydroxide, have a high concentration of phenolate. Since phenols, particularly the alkyl substituted phenols are also comparatively easily soluble in hydrocarbon oils, the problem arises of selecting the composition of the solution in such a manner that the transfer of phenols from the aqueous alkali metal hydroxide solution to the hydrocarbon oil is restricted in such a way that this transfer can practically be neglected or is at any rate so slight that fresh phenols need not be added to the alkali metal hydroxide solution until after prolonged use. lt has now been found that this requirement will be met when the phenolate-containing alkali metal hydroxide solution contains at least 2 mol/liter of free alkali metal hydroxide, i. e. the solution is at least 2 normal (N) in free alkali metal hydroxide, and generally from 2 to 5 mols per liter of free base.

Similar problems arise when an aqueous `phenolatecontaining alkali metal hydroxide solution which has been used for extracting mercaptans from a hydrocarbon oil, without simultaneously using an oxidation agent, is regenerated, for re-use in further extraction, by treating the spent solution containing the mercaptides, in the presence of a light hydrocarbon oil, with oxygen with the result that the `mercaptides are oxidized to disuldes which dissolve in the hydrocarbon oil. In this case too, the transfer of the oxygen from the hydrocarbon oil to the aqueous alkali metal hydroxide solution should be promoted as much as possible and the transfer of phenols from the latter solution to the oil should be prevented as much as possible. in this case the formed disuldes are transferred to, and removed in, the light `hydrocarbon oil utilized in the regeneration. They are subsequently separated from the light hydrocarbons, which latter is recycled to the regeneration zone.

The invention therefore relates in general to a process for converting mercaptans or mercaptides into disuldes by means of oxygen, but without oxidation catalyst, in a two-phase system, one phase of which is formed by a light hydrocarbon oil, particularly gasoline or kerosene, and the other by a stable, homogeneous, `aqueous solution of an alkali metal hydroxide and a phenolate which may or may not be substituted by alkyl groups with a total quantity of not more than three carbon atoms and does not contain other substituents, the two phases being brought into intimate contact with each other, the process Vwith a water content of less than 54% by volume.

3 being characterized in that the aqueous solution contains at most 54% by volume of water and contains at least 2 mols per liter of free alkali metal hydroxide. By light hydrocarbon oil is to ybe understood a hydrocarbon oil the boiling point or end boiling point (the latter in the case of a mixture) of which does not exceed 350 C. The hydrocarbon oil may therefore be gasoline, kerosene or a gas oil. The invention is particularly of importance for processes in which the light hydrocarbon oil is a gasoline or kerosene.

Further description of the invention will be made with reference in part to the accompanying drawing, wherein:

Flg. I is a graph showing the small part of the total ternary. phase diagram water-potassium hydroxide-cresol which 1s employed in the practice of the invention; and

Fig. II is a graph showing the iniluence of composition of the aqueous phase on the rates of oxidation of mercaptans 1n a two-phase system of hydrocarbon an-d the aqueous phase.

The denition which ,is given for the alkali metal hydroxide solutions containing the phenolate means in efect that the process is carried out with solutions which constitute only a small part of the total ternary phase diagram water-alkali metal hydroxide-phenol. For purposes of illustration the area of concentrations under consideration at 20 C. is shown by shading in the graph of Fig. I for the water-potassium hydroxide-cresol system. In the graph the gures along the axes relate to the percentages by weight of the various components. Line AB connectlng the point of 63% KOH on the water-KOH axis with the point of 49.5% cresol on the water-cresol axis corresponds to the line separating the solutions with a water content of more than 54% by volume from the solutions Line BC of the graph shows the limit between solutions which are more than 2-normal of free KOI-l and solutions which are less than Z-normal of free KOH. Finally line CDEA of the graph indicates the limit between the area of the stable homogeneous solutions to be used in the practice of the invention and the area of the unstable solutions or the area in which two or more phases occur side by side in the system under consideration.

If in the water-potassium hydroxide-cresol system of Fig. I the potassium hydroxide is replaced by sodium hydroxide, the area of the concentrations suitable according to the invention is, at the same temperature of, for instance, 20 C. even more limited than in the rst system. This is due to the fact that the curve AEDC separating the area of the stable homogeneous solutions from the area .in which the solutions are supersaturated or separate solid components, is so situated that the area enclosed by the curves AEDC, AB and BC is smaller than when potassium hydroxide is used.

The area ABCDE under consideration of the systems discussed increases with increase of temperature as a result of the displacement of the curve AEDC. On the other hand, the application of solutions which are only stable at comparatively higher temperatures has the disadvantage that such solutions have constantly to be maintained at the higher temperature to prevent the solid components from crystallizing out. Consequently, it is preferable to use such solutions which are stable at room temperature, such as about 20 C., or even at slightly lower temperatures, for instance, C.

In this connection, it is also preferable to use solutions containing potassium hydroxide as the alkali metal hydroxide since at normal operating temperatures these solutions allow a somewhat greater variation with respect to concentrations than solutions containing sodium hydroxide as the alkali metal hydroxide.

The process is preferably carried out at ordinary or slightly elevated temperatures, particularly C.45 C. However, if desired, higher temperatures may be used, for instance, a temperature of 45 C.-80 C., or lower temperatures, for instance, a temperature of 0 C.1,0 C.,

The oxygen required for the process may be supplied to the two-phase system to be treated with it as such or in the form of a mixture of oxygen with another gas that is inert under the operating conditions. Airis a particularly suitable oxygen-containing mixture.

The oxygen may be either dissolved in the hydrocarbon oil in advance or be injected into the hydrocarbon oil vWhile the latter is being brought into contact with the aqueous solution of the alkali metal hydroxide and alkali metal phenate. The quantity of oxygen should at least be equal to the quantity of mercaptans to be oxidized. It is preferred to use an excess of 50%-200% and more particularlyof %-125%, calculated on the quantity of oxygen theoretically require-d to convert the mercaptans (mercaptildes) to disuliides.

If the process is'applied for removing mercaptans from gasoline or kerosene with a content of mercaptan sulphur not exceeding 0.04%-0.05% by weight and the gasoline or kerosene is at equilibrium with the atmosphere, the quantity of oxygen present in the gasoline or kerosene is generally suiicient to effect the desired oxidation. However, the process for removing mercaptans from gasoline and kerosene is frequently carried out shortly after the gasoline or kerosene has been produced from the crude oil and, after any other pretreatments have been carried out, with the result that it is not saturated with air. In that case it is necessary to dissolve air or another oxygencontaining gas in the hydrocarbon oil before or during contact with the caustic alkali solution.

In general the process is carried out un-der atmospheric pressure. If the process is applied for removing mercaptans from hydrocarbon oils with a comparatively high content of mercaptans, for instance a mercaptan sulphur content of 0.04%0.05% by weight or more, using air as oxygen-containing gas, it may be advisable to operate under elevated pressure in order to dissolve an adequate amount of oxygen in the hydrocarbon oil.

In order to promote the transfer of the oxygen from the hydrocarbon phase to the caustic alkali phase in which the oxidation proper takes place, care should be taken to effect an intensive contact between the two phases. This contact can be brought about in various ways, for instance, by means of a centrifugal mixer, a colloid mill; by spraying one phase finely divided into the other; and by the use of packed contacting vessels.

The ratio of the quantity of hydrocarbon oil to the quantity of the caustic alkali phase may vary between Wide limits. The ratio of the volume of the caustic alkali phase to the volume of the hydrocarbon oil may, in general, vary from 0.05 to 5.

When removing the mercaptans from a hydrocarbon oil an advantage of the process is that the desired result can already be obtained by treating the hydrocarbon oil with a quantity of the alkali metal hydroxide and phenolat'e solution described which is considerably lower than the quantity of hydrocarbon oil. In general a quantity of caustic alkali phase of 5%-50% by volume and more particularly of 10%-20% by volume, calculated on the hydrocarbon oil, is very suitable.

If the process is applied for regenerating an alkali metal hydroxide solution containing mercaptides by treating this solution in the presence of a light hydrocarbon oil with oxygen, it is preferable to select the ratio of the volume of the caustic alkali phase to the volume of the hydrocarbon oil between 0.2 and 5 and more particularly between 0.5 and 2.

The process according to the invention may be carried out either continuously or batchwise.

After the hydrocarbon oil and the aqueous solution of alkali metal hydroxide and phenolate have been in contact with each other for a sufficiently long timethey are separated from each other.

When the process is carried out batchwise, the entire quanti-ty of hydrocarbon oil and aqueous solution, which have been in Contact with each other, are allowed to settle until the phases have separated vfrom each other, which occurs after a short time.

When carrying out the pro-:ess continuously, the hydrocarbon oil may be supplied to the aqueous solution of the alkali metal hydroxide and phenolate in such a manner that the oil is in contact with the aqueous solution for a suiciently long time and the continuously discharged hydrocarbon oil passed into a separate settling vessel, in which the entrained aqueous solution separates out and is recycled to the process.

The process may be applied for removing mercaptans from light hydrocarbon oils, particularly gasoline and kerosene, of different origin, including gasoline or kerosene obtained by straight distillation from crude oils as well as gasoline and kerosene obtained from heavy base materials by cracking. The so-called reformed gasoline may also be freed from mercaptans according to the present process. However, when using the process for hydrocarbon oils containing unsaturated components, particular-- ly cracked gasoline and reformed gasoline, it is necessary to add to the oil and anti-oxidant such as an aryl amine or an alkyl phenol, and the alkyl groups of which contain a total of 4 carbon atoms or more to prevent the formation of peroxides and gum from the unsaturated components of the oil. In general a quantity of 0.0001%`- 0.01% by weight of such an anti-oxidant will suice.

Since when applying the process for removing mercaptans from hydrocarbon oils, the disuliides formed during oxidation pass again into the hydrocarbon oil, the process is primarily suitable for treating light hydrocarbon oils with a low mercaptan content, i. e. lower than 0.05% by weight and preferably lower than 0.02% by weight, calculated as mercaptan sulfur. In' this case the quantity of disuliides returned into the hydrocarbonoil is also small. In gasoline a low content of organic disulfides does not appreciably adect its lead susceptibility.

When gasoline or kerosene with a considerable mercaptan sulfur content, for instance, 0.05% by weight or more, is to be freed from mercaptans, the greater portion of the mercaptans, if desired together with other sulfur compounds, may be first removed by any of the hitherto usual methods and then the remainder of the original quantity of mercaptans oxidized according to the process of the invention.

The pretreatment for removing the greater part of the mercaptans may, for example, be elected by extracting (Without oxidation) the hydrocarbon oil with an aqueous alkali metal hydroxide solution containing a solutizer for mercaptans.

More especially, in this latter case it is possible to carry out the pretreatment for extracting (without oxidation) the greater portion of the mercaptans from the hydrocarbon oil with an aqueous solution containing the same alkali metal hydroxide and phenolate wlhich are present in the aqueous solution used in the subsequent treatment, in which the hydrocarbon oil is sweetened by converting the remaining mercaptans into disulphides. The concentration (based upon the water content) of phenolate and also that of alkali metal hydroxide in the aqueous solution used in the pretreatment for extracting mercaptans without oxidation may be somewhatlower than the concentration of phenolate and alkali metal hydroxide in the aqueous solution used in the subsequent step, in which the mercaptans still present in the hydrocarbon oil are converted into disulphides by means of oxygen. For instance, in the said pretreatment a solution containing 45% by weight of water, 35 by weight of KOH and 20% by weight of cresol (which will be present at least for a considerable part in the form of n for converting mercaptans into`disulphides byrneans of oxygen has the following advantage.

During the process there is some consumption of alkali metal hydroxide and phenolate (however, it is to be remarked that in the treatment of hydrocarbon oils rich in phenols the aqueous solution may be enriched with phenols by transfer from the hydrocarbon oil into `the aqueous solution), while moreover the aqueous solution is diluted by the water which is often present in small quantities in the treated hydrocarbon oil as well as by water which is formed by the oxidation of mercaptans (this latter cause of dilution applies to the solution used in the oxidation treatment). When the solution used in the pretreatment for extracting mercaptans without oxidation has a somewhat lower concentration of alkali metal hydroxide and phenolate than the solution used in the subsequent treatment for converting mercaptans into disulphides by oxidation, the former solution may be reconcentrated by the addition of part of the more concentrated solution employed in the subsequent treatment. This latter solution may then be reconcentrated by vthe addition of alkali metal hydroxide and, if necessary, of phenolate. More especially, the rate of adding part of the concentrated solution used in the oxidation treatment to the solution employed in the extraction treatment without oxidation will be so chosen that the total Volume of concentrated solution applied in the oxidation treatment remains constant. In this way the ordinary step of reconcentrating the latter solution by Vaporizing the water with which the solution has been diluted, has become superfluous. It in this way the solution used in the pretreatment for extracting mercaptans without oxidation is not reconcentrated to the desired extent, for example with respect to the amount of phenolate, an additional amount of Ythis constituent may be supplied from another source.

The invention will be illustrated by the following example:

EXAMPLE i n a mixer, which can be considered as a turbomixe'r on a laboratory scale, 8 liters of gasoline were brought into intensive contact with 800 cc. of an aqueous solution of an alkali metal ihydroxide and a phenolate at 20 C.

Various tests were made each time with the same gasoline. This gasoline was a debutanized Venezuelan gasoline obtained by thermal cracking with a boiling range ot 40c C.-240 C. having a mercaptan sulfur content of 0.015% by weight (calculated as elementary sulfur). it should be noted that the sulfur content of this gasoline was mainly present in the form of mercaptans which are diiicult to oxidize. This gasoline Was deliberately chosen since the comparatively slow progress of the oxidation rendered it possible to ascertain the progress of this oxidation in course of time.

Ditterent solutions of alkali metal 'hydroxide and phenolate were used in each of the various tests. The data in Table I show the nature of the alkali metal hydroxide (sodium or potassium hydroxide), the nature of the phenolates (cresolates or xylenolates) the percentages by weight of the various components in the solutions used as Well as the percentage by volume of water calculated therefrom, also the normality of free NaOH or KOH, the number of mol/liter of phenols (which will be actually present as phenolate), the specic gravity and the viscosity at 20 C. (expressed in cs.) of the various solutions.

In connection with the data in Table l, it should be noted that the percentages by weight shown in the fourth and fifth column are calculated as free cresol or xylenol, although this component is present in the solution in the form of the corresponding alkali metal compounds.

The tests were carried out by allowing the impeller of the mixer to run at a circumferential velocity of 2.1 m. per second, with Which the Vsame effect was attained as in a technical turbomixer with a capacity of 10 cubic metres, in which the irnpeller was allowed to run at a circumferential velocity of 4.5 m. per second.

In each of the tests made, a sample of the gasoline was analysed for the mercaptan sulfur content after every 5 minutes, the rst time 5 minutes after putting the apparatus into operation. The total duration of the various tests was 30 minutes.

The last column of the table shows the relative values of the oxidation rates of the mercaptans (mercaptides) measured, the greatest of the oxidation rates measured being given the gure 100.

The results of a number of tests are further illustrated in graph II. In this graph the moment at which the gasoline sample concerned was analysed, is plotted on ythe abscissa. The ordinate relates to the ratio Co/Ct, wherein Co represents the mercaptan concentration in vthe gasoline at the beginning of the test and Ci the mercaptan concentration in the gasoline at the moment when the sample of gasoline was taken.

Graph II relates to tests l0 to 2l inclusive, carried out with aqueous solutions of potassium hydroxide and cresolate or xylenolate. The unbroken lines in the graph relate to the application of cresolate while the dotted lines relate to the use of solutions containing xylenolate.

As will be seen from graph II, the lines illustrating the course of the conversion of the mercaptan sulfur as a function of the time fall apart into two different sets of slopes.

If the composition of the aqueous solutions of alkali metal hydroxide and phenolate used in the various tests is plotted in a phase diagram, such as the one of graph I, the following will be found.

The solutions of alkali metal hydroxide and phenolate with which values of Co/Cf are obtained, which are represented in Fig. II by lines belonging to the bundles with steeper slopes, which means a greater oxidation rate, are in the phase diagram in the area in which the water content of the solutions amounts to less than 54% by volume. On the other hand, the solutions of alkali metal hydroxide and phenolate with which values Cn/ C a are obtained, which are represented in Fig. II by lines belonging to the sets with slighter slopes (lower oxidation rate), are in the phase diagram in the area in which the water content of the solutions amounts to more than 54% by volume.

In tests 1 to 9, which are not shown in Figure II for the sake of simplicity, solutions were used with a water content exceeding 54% by volume. Accordingly, relatively low values were measured for the oxidation rate 4in this case as is shown by the last column of the following table.

Cil

As previously stated, the aqueous alkali metal hydroxf ide solution containing the alkyl phenolate is required to fall within the region of the ternary phase system of a stable homogeneous solution. As will be seen from Fig. I, for the water-KOI-I-cresol system the water content must be at least about 20%, corresponding approximately to the water content on the inside of the region ABCDE at the line CD. For the system water-KOH- xylenol, the corresponding C point is at a water concentration of 25% by weight and the D point is at 30% by weight water. As already stated, the CD line is also displaced toward higher proportions of water in the case of the system: water-NaOH-cresol. Therefore, it is to be seen that the water content in general should be higher than 25% by weight, and preferably it should be at least about 30% by weight.

The invention claimed is:

1. A process for converting mercaptans to disuldes which comprises contacting said mercaptaus with oxygen in the presence of a iirst phase comprising a light hydrocarbon oil intimately admixed with a second phase comprising an aqueous solution of potassium hydroxide and a monohydroxy phenolate which contains only C, H, and O and potassium atoms and which contains from 6 to 9 C-atoms, said aqueous solution containing no more than 54% by volume of water and at least 2 moles of free potassium hydroxide per liter thereof, separating said light hydrocarbon oil and said aqueous solution, and withdrawing an aqueous phase containing said potassium hydroxide and phenolate and an oil phase containing said light hydrocarbon oil and said disuldes.

2. A process for converting mercaptans contained in a light hydrocarbon oil into disuldes which comprises intimately contacting said light hydrocarbon oil in the V presence of oxygen with an aqueous solution of potassium hydroxide and a monohydroxy phenolate, which contains only C, H, O and potassium atoms and which contains from 6 to 9 C-atorns, said aqueous solution containing no more than 54% by volume of water and at least 2 moles of free potassium hydroxide per liter thereof, separating said light hydrocarbon oil and said aqueous solution, and withdrawing an aqueous phase containing said potassium hydroxide and phenolate and an oil phase containing said light hydrocarbon oil and said disuliides.

3. A process according to claim 2, wherein said aqueous solution contains more than 25% by weight of water and contains from 2 to 5 moles of free potassium hydroxide per liter thereof.

4. A process according to claim 3, wherein said light hydrocarbon oil has a boiling range within the boiling range of gasoline and kerosene and has a mercaptan sul- Table l Norm. Mol/ Rela- Test NaOH, KOH, Cresol, Xylenol, Water, Water, NaOH liter Spec. Viscostive No. percent percent percent percent percent percent or Alkyl Gr. ity, Oxida- W. W. w. W. W. v. KOH Phenol es. tion rate l5 50 58. 7 0.60 3. 80 1.174 35. 7 49 19 46 55. 8 1. 84 3. 93 1. 214 76. 5 49 20 50 61. 2 2. 72 3. 40 1. 224 54. 1 49 18 52 62. 7 2.07 3.35 1. 205 35. 8 31 21. 48. 2 59. 3 3.00 3. 50 1. 232 73. 7 31 16. 55.8 66. 3 2. 00 3.00 1.186 20. 5 18 19. 53. 7 65.2 3. O0 3.00 1. 215 31. 3 18 21. 56. 9 70. 0 4.00 2. 50 l. 230 24. 5 18 23. 54. 8 69. 2 5.00 2. 50 1. 261 26. 6 18 34. 8 40. 2 52.0 5.00 3.00 1. 290 9.8 95 33. 0 37. 5 47. 8 4.00 3. 50 1. 273 17. 9 95 fur content no greater than 0.05% by weight, and wherein said phenolate is a cresolate.

5. A process according to claim 1, wherein the contacting temperature is from 0 C. to 80 C.

6. A process according to claim 1, wherein said aqueous solution has been used for extracting mercaptans from a hydrocarbon oil and contains mercaptides extracted from said hydrocarbon oil.

References Cited in the tile of this patent UNITED STATES PATENTS Pevere Sept. 17, 1935 Yabroi July 4, 1939 Yabroi et al. May 28, 1940 Cauley Aug. 3, 1948 

1. A PROCESS FOR CONVERTING MERCAPTANS TO DISULFIDES WHICH COMPRISES CONTACTING SAID MERCAPTANS WITH OXYGEN IN THE PRESENCE OF A FIRST PHASE COMPRISING A LIGHT HYDROCARBON OIL INTIMATELY ADMIXED WITH A SECOND PHASE COMPRISING AN AQUEOUS SOLUTION OF POTASSIUM HYDROXIDE AND A MONOHYDROXY PHENOLATE WHICH CONTAINS ONLY C, H, AND O AND POTASSIUM ATOMS AND WHICH CONTAINS FROM 6 TO 9 C-ATOMS, SAID AQUEOUS SOLUTION CONTAINING NO MORE THAN 54% BY VOLUME OF WATER AND AT LEAST 2 MOLES OF FREE POTASSIUM HYDROXIDE PER LITER THEREOF, SEPARATING SAID LIGHT HYDROCARBON OIL AND SAID AQUEOUS SOLUTION, AND WITHDRAWING AN AQUEOUS PHASE CONTAINING SAID POTASSIUM HYDROXIDE AND PHENOLATE AND AN OIL PHASE CONTAINING SAID LIGHT HYDROCARBON OIL AND SAID DISULFIDES. 